1. Field of the Invention
The present invention relates generally to a magnetic disk drive, and more particularly to a magnetic disk drive having an optimum combination of a magnetic head slider having pads and a magnetic disk surface.
2. Description of the Related Art
In recent years, a reduction in size and an increase in capacity of a magnetic disk drive as a kind of external storage device for a computer have been desired. One method of increasing the capacity of the magnetic disk drive is to increase the number of magnetic disks mounted on a spindle, and in association therewith the spacing between the magnetic disks in a recent magnetic disk drive has increasingly been reduced. In a recent magnetic disk drive, a flying type magnetic head slider adopting a contact start and stop (CSS) system has frequently been used. In such a flying type magnetic head slider adopting the CSS system, a magnetic head slider comes to contact with a magnetic disk when the disk drive stops operation, whereas the magnetic head slider is kept flying at a microscopic height from the disk surface by an air flow generating over the surface of the magnetic disk rotating at a high speed in recording or reproducing information.
In the flying type magnetic head slider adopting the CSS system, an electromagnetic transducer (magnetic head element) is built in the slider for receiving the air flow generating over the disk surface, and the slider is supported by a suspension. Accordingly, when the magnetic disk remains still, the slider including the electromagnetic transducer is in contact with the magnetic disk surface, whereas when the magnetic disk is rotated, a disk opposing surface (flying surface) of the slider opposed to the magnetic disk receives an air flow generated by rotation of the magnetic disk, and the slider flies from the disk surface. The electromagnetic transducer built in the slider is moved over the disk surface as being supported by the suspension to perform recording or reproduction of information at a given track.
In a magnetic disk drive employing a conventional flying type magnetic head slider, a pair of rails are provided on opposite side portions of the disk opposing surface of the magnetic head slider. Each rail has a flat air bearing surface. Further, a tapering surface is formed on each rail at its air inlet end portion. The air bearing surface of each rail receives an air flow generated by high-speed rotation of a magnetic disk to fly the slider and stably maintains a microscopic distance between the disk surface and the electromagnetic transducer.
According to the CSS system, a high flying stability and a microscopic flying height (submicrons) can be ensured. However, when the disk remains still, rail surfaces (air bearing surfaces) of the slider are in contact with the disk. Accordingly, when the magnetic disk drive starts or stops operation, the air bearing surfaces relatively slides on the disk. Accordingly, if the surface roughness of the magnetic disk is small, a contact area of the air bearing surfaces to the magnetic disk surface in the still condition of the magnetic disk is large, so that there arises a problem of stiction between the magnetic head slider and the magnetic disk at starting rotation of the magnetic disk.
To avoid the stiction, the surface roughness of the magnetic disk has conventionally been increased to a suitable level. However, the necessity for further reducing the surface roughness of the magnetic disk has recently been increased to reduce the flying height of the magnetic head slider in response to the requirement for high-density recording. In general, a protective film made of a hard material such as carbon and a lubricating layer for reducing friction and wear of the protective film to improve durability of the magnetic disk are formed on a recording layer of the disk. Owing to the presence of the lubricating layer, friction and wear of the protective film can be reduced. However, when the disk drive stops operation, there is a possibility that stiction between the disk and the slider may occur to cause a problem that the disk drive cannot be restarted.
In association with a recent increase in amount of information, the development in high density, large capacity, and small size of a magnetic disk drive has become remarkable, and the occurrence of stiction has been greatly highlighted as a cause of faulty operation due to a reduction in torque of a spindle motor in association with the size reduction and due to smoothing of the disk surface for the high density. To reduce the stiction between the slider and the disk, it has been proposed to perform crowning of the flying surfaces (rail surfaces) of the slider over the entire length in the longitudinal direction to thereby reduce a contact area between the slider and the disk.
While the slider thus crowned is effective for prevention of the stiction, there is a problem that variations in working accuracy are large and an increase in cost of the slider is invited, so that such a slider is unsuitable for mass production. Further, crowning is performed in the longitudinal direction of each flying surface of the slider, so that each rail surface of the slider becomes nearer to the disk than the electromagnetic transducer (head element) formed on an air inlet end surface of the slider, causing a problem that a spacing loss is produced.
Further, the use of a contact type head intended to attain a zero flying height has recently started to be considered in response to the development in high density, and it is therefore more important to prevent the stiction between the disk and the slider causing faulty operation and fracture of the electromagnetic transducer or the recording layer of the disk. To prevent this stiction problem, it has been proposed to provide a plurality of projections (pads) on the flying surfaces (air bearing surfaces) of the slider, thereby reducing a contact area between the slider and the disk surface (Japanese Patent Laid-open No. 8-69674).
However, the technique disclosed in this publication is characterized in that the contact between the air bearing surfaces of the slider and the magnetic disk surface is avoided by making the projections formed on the air bearing surfaces into sliding contact with the magnetic disk surface. However, there arises another problem of abrasion of the projections formed on the air bearing surfaces due to the sliding contact with the disk surface.
It is therefore an object of the present invention to provide a magnetic disk drive which can effectively avoid the stiction and can suppress the abrasion of the projections on the air bearing surfaces by subjecting the surface of the recording medium to sufficiently controlled texture forming.
It is another object of the present invention to provide a magnetic disk drive which can suppress the generation of dust by suppressing the abrasion of the projections on the air bearing surfaces, thereby achieving high reliability allowing long-term stable operation.
In accordance with an aspect of the present invention, there is provided a magnetic disk drive comprising a housing; a magnetic recording medium rotatably mounted in said housing; a magnetic head slider having an electromagnetic transducer for reading/writing data from/to said magnetic recording medium; and an actuator for moving said magnetic head slider across tracks of said magnetic recording medium; wherein said magnetic head slider has a medium opposing surface opposed to said magnetic recording medium, said medium opposing surface being formed with an air bearing surface and a plurality of projections; and said magnetic recording medium has a unidirectional texture and a surface roughness composed of numerous microscopic projections having an average top radius of 1 xcexcm or more when detected by using a fixed detection length falling in the range of 150 nm to 600 nm.
The above detecting method using the fixed detection length for the surface roughness may be replaced by a method using a threshold height. In this case, the magnetic recording medium has a surface roughness composed of numerous microscopic projections having an average top radius of 1 xcexcm or more when detected by using a fixed threshold height falling in the range of 0.3 nm to 0.5 nm. Preferably, the surface roughness of the magnetic recording medium is defined by an average roughness Ra of 0.3 nm to 3 nm and a maximum height R max of 0.6 nm to 30 nm. The plurality of projections are formed on the air bearing surface or on a portion of the medium opposing surface except the air bearing surface. Preferably, the unidirectional texture is defined as a texture in which microscopic projections each having a minor axis/major axis ratio of 0.05 or less are present in an amount of 45% or more of all microscopic projections.
In accordance with another aspect of the present invention, there is provided a magnetic disk drive comprising a housing; a magnetic recording medium rotatably mounted in said housing; a magnetic head slider having an electromagnetic transducer for reading/writing data from/to said magnetic recording medium; and an actuator for moving said magnetic head slider across tracks of said magnetic recording medium; wherein said magnetic head slider has a medium opposing surface opposed to said magnetic recording medium, said medium opposing surface being formed with an air bearing surface and a plurality of projections; and said magnetic recording medium has a nondirectional texture and a surface roughness composed of numerous microscopic projections having an average top radius of 0.3 xcexcm to 0.75 xcexcm when detected by using a fixed detection length falling in the range of 40 nm to 150 nm.
The above detecting method using the fixed detection length for the surface roughness may be replaced by a method using a threshold height. In this case, the magnetic recording medium has a surface roughness composed of numerous microscopic projections having an average top radius of 0.3 xcexcm to 0.75 xcexcm when detected by using a fixed threshold height falling in the range of 0.3 nm to 0.5 nm. Preferably, the surface roughness of the magnetic recording medium is defined by an average roughness Ra of 0.3 nm to 3 nm and a maximum height R max of 0.6 nm to 30 nm. The plurality of projections are formed on the air bearing surface or on a portion of the medium opposing surface except the air bearing surface. Preferably, the nondirectional texture is defined as a texture in which microscopic projections each having a minor axis/major axis ratio of 0.5 or more are present in an amount of 55% or more of all microscopic projections, and the average top radius is defined as an average of top radii of the microscopic projections measured along their major axes.
The above and other objects, features and advantages of the present invention and the manner of realizing them will become more apparent, and the invention itself will best be understood from a study of the following description and appended claims with reference to the attached drawings showing some preferred embodiments of the invention.